November 20, 2013

Lithium-Sulfur Batteries Could Be The Next Big Thing

A new lithium-sulfur battery may now take the crown as the highest performing battery, lasting more than twice as long as lithium-ion batteries.

Researchers at the U.S. Department of Energy’s Lawrence Berkeley National Laboratory (Berkeley Lab) have shown that lithium-sulfur (Li/S) batteries contain more than twice the energy of lithium-ion, and can last for more than 1,500 charge-discharge cycles. This battery may help to change the game in electric and hybrid vehicles.

“Our cells may provide a substantial opportunity for the development of zero-emission vehicles with a driving range similar to that of gasoline vehicles,” said Elton Cairns, of the Environmental Energy Technologies Division (EETD) at Berkeley Lab.

The battery could provide a cell-level specific energy of 350 to 400 Watt-hours for electric vehicles, giving them a 300-mile range. This would be almost double the specific energy of current lithium-ion batteries.

Researchers wrote in the journal Nano Letters that the battery showed an estimated cell-specific energy of more than 500 Watt-hours and it maintained it at less than 300 Watt-hours after 1,000 cycles, which is much higher than currently available lithium-ion batteries.

“It’s the unique combination of these elements in the cell chemistry and design that has led to a lithium-sulfur cell whose performance has never been achieved in the laboratory before - long life, high rate capability, and high cell-level specific energy,” says Cairns.

The Li/S batteries would be cheaper than current lithium-ion batteries, and they would be less prone to the safety problems that have plagued currently available batteries, such as overheating.

“The lithium-sulfur battery chemistry has attracted attention because it has a much higher theoretical specific energy than lithium-ion batteries do,” says Cairns. “Lithium-sulfur batteries would also be desirable because sulfur is nontoxic, safe and inexpensive.”

The team has met a few challenges in developing the Li/S batteries. They say that during discharge, lithium polysulfides tend to dissolve from the cathode in the electrolytes and react with the lithium anode, forming a barrier layer. This chemical degradation is one reason why the cell capacity begins fading after a few cycles.

Another problem the team experienced with the high performance batteries is that the conversion reaction from sulfur to Li2S and back causes the volume of the sulfur electrode to swell and contract up to 76 percent during cell operation.

The scientists say they are now seeking support for the continuing development of the Li/S cell, including higher sulfur utilization, operations under extreme conditions, and scale-up. The next step will be to try to further increase the cell energy density, improve cell performance under extreme conditions, and scale up to larger cells.